let str = `abcdedfghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890`;

let rnd = 0;
let len = str.length;
for (let j = 0;j < 7; j ++) {
  let rs = '';
  for (let i = 0; i < 24; i++) {
    rnd = Number.parseInt(Math.random() * len);
    rs += str[rnd];
  }
  console.log(rs);
}
